With the availability of increased data processing capability and mass storage systems, it is imperative that data communication links transfer large amounts of data at significantly increased rates. The Fiber Distributed Data Interface (FDDI) provides a standard for high speed fiber optic data communication used in local area network applications as a high performance interconnection among mainframe computers, their mass storage sub-systems and other peripheral digital devices. According to the FDDI standard as defined by the American National Standards Institute, data traffic on the high speed network may approach data transmission rates of approximately 125 Megabits per second. The standard also requires a Bit Error rate of 2.5.times.10.sup.-10 which corresponds to a signal to noise ratio of about 6:1.
To accomplish accurate and reliable data transmission at FDDI specified data rates, FDDI compatible fiber optic components currently provide the data transmission media. While such components operate accurately and effectively, implementation of the fiber optic transmission network is costly. This cost is magnified in an office environment where numerous workstations and other digital devices are located within a relatively local geographical area. In many applications, the higher speed fiber optic network replaces an existing lower speed network operating over a coaxial or twisted pair media. Thus, the cost of implementing the fiber optic network includes the removal of the already existing network.
It is therefore desirable to provide a less expensive option to the high cost fiber optic components comprising the transmission system particularly for shorter data links. It has been found that coaxial components provide a cost savings on the order of twenty to one in comparison with optical components. Moreover, it is advantageous to implement an FDDI network using an already installed coaxial media to upgrade existing networks designed to operate at lower data rates. It is also desirable to use twisted pair media in an FDDI network as a cost saving alternative and for maximum flexibility.
The use of a single coaxial media for bidirectional data transmission is known for application at lower frequencies, for example in telephonic or voice communication. However, significant constraints on these devices prohibit transmission over coaxial media in conformance with the FDDI standard. The use of twisted pair media as the transmission medium for FDDI data communication is likewise heretofore unknown.
Collision detection is another approach to bidirectional transmission. This approach involves biasing packets of data at a predetermined DC voltage level. The simultaneous transmission of two or more packets creates an increased DC voltage level. The collision detection approach, however, requires additional collision handling algorithms that are time consuming and do not conform with the FDDI standard. Therefore, a need exists to provide a transmission media for FDDI data at a lower cost yet conforms to the requirements of the FDDI standard.